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Tiger shark
The tiger shark (Galeocerdo cuvier) is a species of requiem shark and the only extant member of the genus Galeocerdo. Commonly known as the "Sea Tiger" and as "the garbage can of the sea", the tiger shark is a relatively large macropredator, capable of attaining a length over 5 m (16 ft 5 in), with some reputed to reach a length of over 7 m (23 ft) or more. It is found in many tropical and temperate waters, and it is especially common around central Pacific islands. Its name derives from the dark stripes down its body which resemble a tiger's pattern, which fade as the shark matures. The tiger shark is a solitary, mostly nocturnal hunter, and is notable for having the widest food spectrum of all sharks, consuming a variety of prey ranging from crustaceans, fish, seals, birds, squid, turtles, and sea snakes to dolphins and even other smaller sharks. The tiger shark has been known to eat inedible, man-made objects that linger in its stomach, and it has a reputation as a "garbage eater". While the tiger shark sits atop the food chain as an apex predator, killer whales have been known on occasion to prey on them. The tiger shark is considered a near threatened species due to finning and fishing by humans. Taxonomy The tiger shark was first described by Peron and Lesueur in 1822, and was given the name Squalus cuvier. Müller and Henle in 1837 renamed it Galeocerdo tigrinus. The genus, Galeocerdo, is derived from the Greek galeos, which means shark, and the Latin cerdus, the word for the hard hairs of pigs. It is often colloquially called the man-eater shark. The tiger shark is a member of the order Carcharhiniformes, the most species-rich order of sharks, with more than 270 species also including the small catsharks and hammerhead sharks. Members of this order are characterized by the presence of a nictitating membrane over the eyes, two dorsal fins, an anal fin, and five gill slits. It is the largest member of the Carcharhinidae family, commonly referred to as requiem sharks. This family consists of mostly slender but powerful mid- to large-sized sharks and includes some other well-known sharks, such as the blue shark (Prionace glauca), lemon shark (Negaprion brevirostris), and bull shark (Carcharhinus leucas). Description The tiger shark commonly attains a length of 3.25–4.25 m (10 ft 8 in–13 ft 11 in) and weighs around 385–635 kg (849–1,400 lb). Sometimes, an exceptionally large male tiger shark can grow up to 4 m (13 ft 1 in). Females are larger, and exceptionally big ones can reportedly measure over 5 m (16 ft 5 in). Weights of particularly large female tiger sharks can reach and exceed 900 kg (2,000 lb). One female specimen caught off Australia reportedly measured 5.5 m (18 ft 1 in) long and weighed an exceptional 1,524 kg (3,360 lb), although her weight is thought to have been bolstered by her pregnant state at the time. Even larger specimens have been reported, but are considered as unconfirmed. Some papers have accepted a record of an exceptional 7.4 m (24 ft 3 in) length for a tiger shark, but since this is far larger than any scientifically observed specimen, verification would be needed. Among the largest extant sharks, the tiger shark ranks in average size only behind the whale shark (Rhincodon typus), the basking shark (Cetorhinus maximus), and the great white shark (Carcharodon carcharias). Some other species such as megamouth sharks (Megachasma pelagios), Pacific sleeper sharks (Somniosus pacificus), Greenland sharks (Somniosus microcephalus), and bluntnose sixgill sharks (Hexanchus griseus) broadly overlap in size with the tiger shark, but as these species are comparatively poorly studied, it is unclear whether their typical mature size matches that of the tiger shark. The great hammerhead (Sphyrna mokarran), a member of the same taxonomic order as the tiger shark, has a similar or even greater average body length, but is lighter and less bulky, with a maximum known weight of 580 kg (1,280 lb). Tiger shark teeth are unique with very sharp, pronounced serrations and an unmistakable sideways pointing tip. Such dentition has developed to slice through flesh, bone, and other tough substances such as turtle shells. Like most sharks, its teeth are continually replaced by rows of new teeth throughout the sharks life. Relative to the shark's size, tiger shark teeth are considerably shorter than those of a great white shark, however they are nearly as broad as the root as the great whites teeth and are arguably better suited to slicing through hard-surfaced prey. As its teeth are better built for slicing through tough-skinned prey, the tiger shark also lacks the same bite force as the great white, and has significantly weaker jaws in comparison. Skin The skin of a tiger shark can typically range from blue to light green with a white or light-yellow underbelly. The advantage of this is that when it is hunting for its prey, when prey looks at the shark from above, the shark will be camouflaged since the water below is darker. And when prey is below the shark and looks up, of course because of the sun, it is lighter so that the light underbelly will also camouflage the shark. This is known as countershading. Dark spots and stripes are most visible in young sharks and fade as the shark matures. Its head is somewhat wedge-shaped, which makes it easy to turn quickly to one side. They have small pits on the snout which hold electroreceptors called the ampullae of Lorenzini, which enable them to detect electric fields, including the weak electrical impulses generated by prey, which helps them to hunt. Tiger sharks also have a sensory organ called a lateral line which extends on their flanks down most of the length of their sides. The primary role of this structure is to detect minute vibrations in the water. These adaptations allow the tiger shark to hunt in darkness and detect hidden prey. Vision A reflective layer behind the tiger shark's retina, called the tapetum lucidum, allows light-sensing cells a second chance to capture photons of visible light, enhancing vision in low-light conditions. A tiger shark generally has long fins to provide lift as the shark maneuvers through water, while the long upper tail provides bursts of speed. The tiger shark normally swims using small body movements. Its high back and dorsal fin act as a pivot, allowing it to spin quickly on its axis, though the shark's dorsal fins are distinctively close to its tail. Diet The tiger shark is an apex predator and has a reputation for eating anything. These predators swim close inland to eat at night, and during the day swim out into deeper waters. Young tiger sharks are found to prey largely on small fish, as well as various small jellyfish, cephalopods, and other mollusks. Around the time they attain 2.3 m (7.5 ft), or near sexual maturity, their prey selection expands considerably, and much larger animals become regular prey. Numerous fish, crustaceans, sea birds, sea snakes, marine mammals (such as bottlenose dolphins (Tursiops), common dolphins (Delphinus), spotted dolphins (Stenella), dugongs (Dugong dugon), seals and sea lions, and sea turtles (including the three largest species: the leatherback (Dermochelys coriacea), the loggerhead (Caretta caretta) and the green sea turtles (Chelonia mydas),) are regularly eaten by adult tiger sharks. In fact, adult sea turtles have been found in up to 20.8% of studied tiger shark stomachs, indicating somewhat of a dietary preference for sea turtles where they are commonly encountered. They also eat other sharks (including adult sandbar sharks (Carcharhinus plumbeus)), as well as rays, and sometimes even eat other tiger sharks. Due to high risk of predatory attacks, dolphins often avoid regions inhabited by tiger sharks. They may also attack injured or ailing whales and prey upon them. A group was documented attacking and killing an ailing humpback whale (Megaptera novaeangliae) in 2006 near Hawaii. The tiger shark also scavenges on dead whales. In one such documented incident, they were observed scavenging on a whale carcass alongside great white sharks. Evidence of dugong predation was identified in one study that found dugong tissue in 15 of 85 tiger sharks caught off the Australian coast. Additionally, examination of adult dugongs has shown scars from failed shark attacks. Finally, dugong microhabitats shift similarly to those of known tiger shark prey when the sharks are abundant. The broad, heavily calcified jaws and nearly terminal mouth, combined with robust, serrated teeth, enable the tiger shark to take on these large prey. In addition, excellent eyesight and acute sense of smell enable it to react to faint traces of blood and follow them to the source. The ability to pick up low-frequency pressure waves enables the shark to advance towards an animal with confidence, even in murky water. The shark circles its prey and studies it by prodding it with its snout. When attacking, the shark often eats its prey whole, although larger prey are often eaten in gradual large bites and finished over time. Notably, terrestrial mammals, including horses (Equus ferus caballus), goats (Capra aegagrus hircus), sheep (Ovis aries), dogs (Canis lupus familiaris), cats (Felis catus), and brown rats (Rattus norvegicus), are fairly common in the stomach contents of tiger sharks around the coasts of Hawaii. In one case, remains of two flying foxes were found in the stomach of this shark. Because of its aggressive and indiscriminate feeding style, it often mistakenly eats inedible objects, and such items found in its stomach include objects such as automobile license plates, oil cans, tires, tennis shoes, nuts and bolts, baseballs, cigarettes, coconuts, and even segments from a suit of medieval armor. Swimming efficiency and stealth All tiger sharks generally swim slowly, which, combined with cryptic coloration, may make them difficult for prey to detect in some habitats. They are especially well camouflaged against dark backgrounds. Despite their sluggish appearance, tiger sharks are one of the strongest swimmers of the carcharhinid sharks. Once the shark has come close, a speed burst allows it to reach the intended prey before it can escape. Reproduction Males reach sexual maturity at 2.3 to 2.9 m (7.5 to 9.5 ft) and females at 2.5 to 3.5 m (8.2 to 11.5 ft). Average weight of relatively young sexual mature specimens, which often locally comprise the majority of tiger sharks encountered per game-fishing and scientific studies, is around 80 to 130 kg (180 to 290 lb). Females mate once every three years. They breed by internal fertilization. The male inserts one of his claspers into the female's genital opening (cloaca), acting as a guide for the sperm. The male uses his teeth to hold the female still during the procedure, often causing the female considerable discomfort. Mating in the Northern Hemisphere generally takes place between March and May, with birth between April and June the following year. In the Southern Hemisphere, mating takes place in November, December, or early January. The tiger shark is the only species in its family that is ovoviviparous; its eggs hatch internally and the young are born live when fully developed. The young develop inside the mother's body up to 16 months. Litters range from 10 to 80 pups. A newborn is generally 51 to 76 cm (20 to 30 in) long. How long tiger sharks live is unknown, but they can live longer than 12 years. Conservation The tiger shark is captured and killed for its fins, flesh, and liver. It is caught regularly in target and nontarget fisheries. Several populations have declined where they have been heavily fished. Continued demand for fins may result in further declines in the future. They are considered a near threatened species due to excessive finning and fishing by humans according to International Union for Conservation of Nature. While shark fin has very few nutrients, shark liver has a high concentration of vitamin A which is used in the production of vitamin oils. In addition, the tiger shark is captured and killed for its distinct skin, as well as by big-game fishers. In 2010, Greenpeace International added the tiger shark to its seafood red list, which is a list of fish commonly sold around the world, and which have a very high risk of being sourced from unsustainable fisheries. Relationship with Humans Although sharks rarely bite humans, the tiger shark is reported to be responsible for a large percentage of fatal shark bite incidents, and is sometimes regarded as one of the most dangerous shark species. They often visit shallow reefs, harbors, and canals, creating the potential for encounter with humans. The tiger shark also dwells in river mouths and other runoff-rich water. While the tiger shark is considered to be one of the sharks most dangerous to humans, its bite rate is low. It is second on the list of number of recorded bites on humans, with the great white shark being first. On average, three to four shark bites occur per year in Hawaii, but they are rarely fatal. This bite rate is very low considering thousands of people swim, surf, and dive in Hawaiian waters every day. Human interactions with tiger sharks in Hawaiian waters have been shown to increase between September and November, when tiger shark females are believed to migrate to the islands to give birth. Unlike the great white, which often releases humans upon attacking them, the tiger shark is known to prey on humans due to their presenting an opportunity to feed on vulnerable and helpless prey. Several tiger shark attacks recorded have involved the shark both killing and devouring its intended victim, with the shark completely consuming the victim. Between 1959 and 2000, 4,668 tiger sharks were culled in an effort to protect the tourism industry. These efforts, despite damaging the shark population, were shown to be ineffective in decreasing the number of interactions between humans and tiger sharks. Feeding sharks in Hawaii (except for traditional Hawaiian cultural or religious practices) is illegal, and interaction with them, such as cage diving, is discouraged. South African shark behaviorist and shark diver Mark Addison demonstrated divers could interact and dive with them outside of a shark cage in a 2007 Discovery Channel special, and underwater photographer Fiona Ayerst swam with them in the Bahamas. At "Tiger Beach" off Grand Bahama, uncaged diving with - and even the handling of - female tiger sharks has become a routine occurrence. Impact in Mythology The tiger shark is considered to be sacred na ʻaumakua (ancestor spirits) by some native Hawaiians who think their eyeballs have special powers of visual perception. This aligns with the generally known facts about sharks and their highly developed senses. In Popular Culture The tiger shark is well known in popular culture, and in many stories, takes the place of the great white. Among its many appearances, notable examples include the children's show Kenny the Shark, which focuses on an anthropomorphic, amphibious tiger shark named Kenny as its main protagonist, Tintorera, which focuses on a man-eating tiger shark, the Syfy film Spring Break Shark Attack,and the video games Shark: Hunting the Great White, and ''Depth''. In Depth, the tiger shark has the ability to camouflage itself so as to render it untraceable and invisible to divers' equipment for 30 seconds, allowing it to perform sneak attacks on enemies. Category:Chondrichthyes Category:Elasmobranchs Category:Sharks Category:Carcharhiniformes Category:Carcharhinidae Category:Galeocerdo Category:Near Threatened Species